The invention concerns a procedure for cleaning a double seat valve under the heading of claim 1 and a valve arrangement for implementing the procedure under the heading of claim 8 or 9. A method of the type characterized above is known from DE 31 08 778 C2. This procedure solves the problem of cleaning both seat surfaces of the closing members in a valve of the type under discussion simultaneously. In doing so, the cleansing and/or disinfecting agent is introduced either from outside the double seat valve through the leakage hollow space or through a valve housing part to both exposed seats (compare FIGS. 1-5a of the drawings).
In EP-A-0 208 126, the procedure known from DE 31 08 778 C 2 is further developed in such a way that in a double seat valve equipped with a slider and a seat plate, for the purposes of cleaning the seat of the slide type closing member, the seat is movable only in the direction of the associated valve housing, while the seat plate remains on its seat surface. The cleansing agent is introduced from outside of the double seat valve via the leakage hollow space to the exposed seating surface. This as well as the older procedure contributes to cleansing a relevant double seat valve area, namely the seat area. Nonetheless, in practice it is necessary to include other relevant areas in the cleaning procedure, those of the rod passage guides through the associated valve housing parts.
In valves with slide type closing members, it is necessary to take special precautions so that the compressive forces exerted by the fluid in the conduits upon the closing members can be absorbed. These forces may be compensated for either through suitable measures in the valve drive or through pressure compensating measures on the closing member in the valve housing area (cf. EP-A-00 39 319, FIG. 1; EP-A-0 208 126, FIG. 3.2). The former measure leads to driving gears of relatively large dimensions, while pressure-compensating measures on the closing member naturally require large rod guide passages, which are problematic simply because of their large sealing length with regard to their ability to be cleansed and their safety with reference to mixing product and cleaning fluid.
It is known from EP-A-00 39 319 that a chamber should be placed between the seals of the pressure compensating piston which can be rinsed by cleansing agents. In order to ensure sufficient cleansing agent throughput, there must be a sufficiently large static pressure where the cleansing agent enters. Nonetheless, for safety reasons, it is generally desirable that the cleansing agent is subject to as little pressure as possible on the rod seal facing the interior area of the valve housing. In any case, one must nonetheless take care that at certain time intervals the area behind the seal, with its relatively large circumferential length (into which, because of the actuating movement of the valve, product can occasionally be dragged), and the contact surfaces between seal and rod can be subjected to or irrigated by cleansing agents. It is shown in DE 37 01 027 A1(cf. FIGS. 7 and 8) how two particular sealing points arranged in series on the side of the housing which act together with a slide type closing member whose intermediate space can be rinsed from time to time in the area of one of the sealing points without having to expose the entire seating area of the closing member. While the previously cited figures show a one piece seal with two sealing points, the possibility of seal arrangements with two separate seals follows from the introduction of the description and the claims. Separate cleansing of two seals arranged at a distance on the side of the housing interacting with a slide-like closing member, or with a rod guided out of the valve housing by a partial displacement of the closing member or of the rod for the purpose of exposing one or the other seal to the valve housing part which contains the cleansing agent is explained in greater detail in publication W 0 88/05512(cf. e.g. FIGS. 21, 22; 25, 26 and 59, 60), which claims priority for the above named DE 37 01 0027.
Finally, it is clear from publication DE-U- 88 13 258 how a double seat valve having a closing member constructed as a seat plate and as a slider where the compressive forces on the slider are compensated by a pressure compensation cylinder constructed on the slider can be subjected to a cleansing in the seat region of the slider and in that of the pressure compensation piston guide passage through the valve housing parts with results known from the previously cited publications. It is clear that two parallel cleansing streams (r.sub.1, r.sub.2) branch off from the lower valve housing part. The one (r.sub.1) proceeds to the valve region through the exposed seat surface of the slide type closing member over the leakage hollow space and a pipe leading downward from the valve housing part. The other stream (r.sub.2) proceeds to this region over the exposed guide for the pressure compensation piston out of the valve housing part.
This well known solution possesses several disadvantages. First, the cleanser stream (r.sub.1) which passes through the exposed seat surface of the slide type closing member is difficult to measure, meaning that an uncontrolled waste of cleanser with an associated environmental pollution is not impossible. Second, a second parallel cleanser stream (r.sub.2) is necessary to cleanse an additional critical area of the double seat valve, the guide passage area of the pressure compensation piston of the one closing member. In addition, further equally critical areas of the double seat valve remain uncleansed. These areas are, under certain circumstances, the seat area of the closing member constructed as a seat plate, which occasionally comes into contact with product. In any case, these areas include the guide of the closing member activation rod through the overlying valve housing part and the sealing area between the activation rod of the slider-form closing member and the seat plate pipe surrounding this rod.